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Exploring the ferromagnetic behaviour of a repulsive Fermi gas through spin dynamics

Abstract

Ferromagnetism is a manifestation of strong repulsive interactions between itinerant fermions in condensed matter. Whether short-ranged repulsion alone is sufficient to stabilize ferromagnetic correlations in the absence of other effects, such as peculiar band dispersions or orbital couplings, is, however, unclear. Here, we investigate ferromagnetism in the minimal framework of an ultracold Fermi gas with short-range repulsive interactions tuned via a Feshbach resonance. Whereas fermion pairing characterizes the ground state, our experiments provide signatures suggestive of a metastable Stoner-like ferromagnetic phase supported by strong repulsion in excited scattering states. We probe the collective spin response of a two-spin mixture engineered in a magnetic domain-wall-like configuration, and reveal a substantial increase of spin susceptibility while approaching a critical repulsion strength. Beyond this value, we observe the emergence of a time window of domain immiscibility, indicating the metastability of the initial ferromagnetic state. Our findings establish an important connection between dynamical and equilibrium properties of strongly correlated Fermi gases, pointing to the existence of a ferromagnetic instability.

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Figure 1: Engineering a ferromagnetic state with an ultracold atomic Fermi gas.
Figure 2: Spin response of a repulsive Fermi gas.
Figure 3: Metastability of a fully magnetized ultracold Fermi gas.
Figure 4: Spin drag coefficient of a strongly interacting Fermi gas.

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References

  1. Vollhardt, D., Blumer, N. & Kollar, M. Metallic Ferromagnetism—An Electronic Correlation Phenomenon Vol. 580 (Lecture Notes in Physics, Springer, 2001).

    Book  Google Scholar 

  2. Brando, M., Belitz, D., Grosche, F. M. & Kirkpatrick, T. R. Metallic quantum ferromagnets. Rev. Mod. Phys. 88, 025006 (2016).

    Article  ADS  Google Scholar 

  3. Vollhardt, D. & Wölfle, P. The Superfluid Phases of Helium-3 (Taylor and Francis, 1990).

    Book  Google Scholar 

  4. Silverstein, S. D. Criteria for ferromagnetism in dense neutron Fermi liquids-neutron stars. Phys. Rev. Lett. 23, 139–141 (1969).

    Article  ADS  Google Scholar 

  5. Tatsumi, T. Ferromagnetism of quark liquid. Phys. Lett. B 489, 280–286 (2000).

    Article  ADS  Google Scholar 

  6. Stoner, E. Atomic moments in ferromagnetic metals and alloys with non-ferromagnetic elements. Philos. Mag. 15, 1018–1034 (1933).

    Article  Google Scholar 

  7. Saxena, S. S. et al. Superconductivity on the border of itinerant-electron ferromagnetism in UGe2 . Nature 406, 587–592 (2000).

    Article  ADS  Google Scholar 

  8. Pfleiderer, C., Julian, S. R. & Lonzarich, G. G. Non-Fermi-liquid nature of the normal state of itinerant-electron ferromagnets. Nature 414, 427–430 (2001).

    Article  ADS  Google Scholar 

  9. Chin, C., Grimm, R., Julienne, P. S. & Tiesinga, E. Feshbach resonances in ultracold gases. Rev. Mod. Phys. 82, 1225–1286 (2010).

    Article  ADS  Google Scholar 

  10. Shenoy, V. B. & Ho, T.-L. Nature and properties of a repulsive Fermi gas in the upper branch of the energy spectrum. Phys. Rev. Lett. 107, 210401 (2011).

    Article  ADS  Google Scholar 

  11. Kohstall, C. et al. Metastability and coherence of repulsive polarons in a strongly interacting Fermi mixture. Nature 485, 615–618 (2012).

    Article  ADS  Google Scholar 

  12. Massignan, P., Zaccanti, M. & Bruun, G. M. Polarons, dressed molecules, and itinerant ferromagnetism in ultracold Fermi gases. Rep. Prog. Phys. 77, 034401 (2014).

    Article  ADS  Google Scholar 

  13. Sanner, C. et al. Correlations and pair formation in a repulsively interacting Fermi gas. Phys. Rev. Lett. 108, 240404 (2012).

    Article  ADS  Google Scholar 

  14. Lee, Y. et al. Compressibility of an ultracold Fermi gas with repulsive interactions. Phys. Rev. A 85, 063615 (2012).

    Article  ADS  Google Scholar 

  15. Pekker, D. et al. Competition between pairing and ferromagnetic instabilities in ultracold fermi gases near Feshbach resonances. Phys. Rev. Lett. 106, 050402 (2011).

    Article  ADS  Google Scholar 

  16. Duine, R. A. & MacDonald, A. H. Itinerant ferromagnetism in an ultracold atom Fermi gas. Phys. Rev. Lett. 95, 230403 (2005).

    Article  ADS  Google Scholar 

  17. LeBlanc, L. J., Thywissen, J. H., Burkov, A. A. & Paramekanti, A. Repulsive Fermi gas in a harmonic trap: ferromagnetism and spin textures. Phys. Rev. A 80, 013607 (2009).

    Article  ADS  Google Scholar 

  18. Conduit, G. J., Green, A. G. & Simons, B. D. Inhomogeneous phase formation on the border of itinerant ferromagnetism. Phys. Rev. Lett. 103, 207201 (2009).

    Article  ADS  Google Scholar 

  19. Cui, X. & Zhai, H. Stability of a fully magnetized ferromagnetic state in repulsively interacting ultracold Fermi gases. Phys. Rev. A 81, 041602(R) (2010).

    Article  ADS  Google Scholar 

  20. Pilati, S., Bertaina, G., Giorgini, S. & Troyer, M. Itinerant ferromagnetism of a repulsive atomic Fermi gas: a quantum Monte Carlo study. Phys. Rev. Lett. 105, 030405 (2010).

    Article  ADS  Google Scholar 

  21. Chang, S., Randeria, M. & Trivedi, N. Ferromagnetism in the upper branch of the Feshbach resonance and the hard-sphere Fermi gas. Proc. Natl Acad. Sci. USA 108, 51–54 (2011).

    Article  ADS  Google Scholar 

  22. Jo, G. et al. Itinerant ferromagnetism in a Fermi gas of ultracold atoms. Science 325, 1521–1524 (2009).

    Article  ADS  Google Scholar 

  23. Scazza, F. et al. Repulsive Fermi polarons in a resonant mixture of ultracold 6Li atoms. Phys. Rev. Lett. 118, 083602 (2017).

    Article  ADS  Google Scholar 

  24. Schmidt, R. & Enss, T. Excitation spectra and RF response near the polaron-to-molecule transition from the functional renormalization group. Phys. Rev. A 83, 063620 (2011).

    Article  ADS  Google Scholar 

  25. Recati, A. & Stringari, S. Spin fluctuations, susceptibility and the dipole oscillation of a nearly ferromagnetic Fermi gas. Phys. Rev. Lett. 106, 080402 (2011).

    Article  ADS  Google Scholar 

  26. Sommer, A., Ku, M., Roati, G. & Zwierlein, M. Universal spin transport in a strongly interacting Fermi gas. Nature 7342, 201–204 (2011).

    Article  ADS  Google Scholar 

  27. Enss, T. & Haussmann, R. Quantum mechanical limitations to spin diffusion in the unitary Fermi gas. Phys. Rev. Lett. 109, 195303 (2012).

    Article  ADS  Google Scholar 

  28. Bardon, A. B. et al. Transverse demagnetization dynamics of a unitary Fermi gas. Science 344, 722–724 (2014).

    Article  ADS  Google Scholar 

  29. Burchianti, A. et al. Efficient all-optical production of large 6Li quantum gases using D1 gray-molasses cooling. Phys. Rev. A 90, 043408 (2014).

    Article  ADS  Google Scholar 

  30. Valtolina, G. et al. Josephson effect in fermionic superfluids across the BEC–BCS crossover. Science 350, 1505–1508 (2015).

    Article  ADS  MathSciNet  Google Scholar 

  31. Zürn, G. et al. Precise characterization of 6Li Feshbach resonances using trap-sideband-resolved RF spectroscopy of weakly bound molecules. Phys. Rev. Lett. 110, 135301 (2013).

    Article  ADS  Google Scholar 

  32. Bienaimé, T. et al. Spin-dipole oscillation and polarizability of a binary Bose-Einstein condensate near the miscible-immiscible phase transition. Phys. Rev. A 94, 063652 (2016).

    Article  ADS  Google Scholar 

  33. Sanner, C. et al. Speckle imaging of spin fluctuations in a strongly interacting Fermi gas. Phys. Rev. Lett. 106, 010402 (2011).

    Article  ADS  Google Scholar 

  34. Meineke, J. et al. Interferometric measurement of local spin fluctuations in a quantum gas. Nat. Phys. 8, 454–458 (2012).

    Article  Google Scholar 

  35. Duine, R. A., Polini, M., Stoof, H. T. C. & Vignale, G. Spin Drag in an ultracold Fermi gas on the verge of ferromagnetic instability. Phys. Rev. Lett. 104, 220403 (2010).

    Article  ADS  Google Scholar 

  36. Taylor, E., Zhang, S., Schneider, W. & Randeria, M. Colliding clouds of strongly interacting spin-polarized fermions. Phys. Rev. A 84, 063622 (2011).

    Article  ADS  Google Scholar 

  37. Nascimbene, S. et al. Fermi-Liquid behavior of the normal phase of a strongly interacting gas of cold atoms. Phys. Rev. Lett. 106, 215303 (2011).

    Article  ADS  Google Scholar 

  38. Tajima, H., Hanai, R. & Ohashi, Y. Strong-coupling corrections to spin susceptibility in the BCS–BEC-crossover regime of a superfluid Fermi gas. Phys. Rev. A 93, 013610 (2016).

    Article  ADS  Google Scholar 

  39. Goulko, O., Chevy, F. & Lobo, C. Collision of two spin-polarized fermionic clouds. Phys. Rev. A 84, 051605 (2011).

    Article  ADS  Google Scholar 

  40. Elliott, E., Joseph, J. A. & Thomas, J. E. Anomalous minimum in the shear viscosity of a Fermi gas. Phys. Rev. Lett. 113, 020406 (2014).

    Article  ADS  Google Scholar 

  41. Trotzky, S. et al. Observation of the Leggett–Rice effect in a unitary Fermi gas. Phys. Rev. Lett. 114, 015301 (2015).

    Article  ADS  Google Scholar 

  42. Levinsen, J. & Parish, M. M. in Annual Reviews of Cold Atoms and Molecules Vol. 3 (eds Madison, K. W. et al.) Ch. 1, 1–75 (World Scientific, 2015).

    Book  Google Scholar 

  43. Pilati, S., Zintchenko, I. & Troyer, M. Ferromagnetism of a repulsive atomic Fermi gas in an optical lattice: a quantum Monte Carlo study. Phys. Rev. Lett. 112, 015301 (2014).

    Article  ADS  Google Scholar 

  44. Pilati, S. & Fratini, E. Ferromagnetism in a repulsive atomic Fermi gas with correlated disorder. Phys. Rev. A 93, 051604(R) (2016).

    Article  ADS  Google Scholar 

  45. He, L., Liu, X.-J., Huang, X.-G. & Hu, H. Stoner ferromagnetism of a strongly interacting Fermi gas in the quasirepulsive regime. Phys. Rev. A 93, 063629 (2016).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

We thank A. Morales and J. Seman for contributions in the early stage of the experiment, and G. Bertaina, G. M. Bruun, C. Di Castro, C. Fort, S. Giorgini, R. Grimm, W. Ketterle, P. Massignan, S. Pilati, R. Schmidt, W. Zwerger, M. Zwierlein and the LENS Quantum Gases group for many stimulating discussions. We thank H. Tajima and Y. Ohashi for providing us recent data of the lower branch spin susceptibility. This work was supported under European Research Council grants no. 307032 QuFerm2D, and no. 637738 PoLiChroM. A.R. acknowledges support from the Alexander von Humboldt Foundation. T.E. acknowledges the Physics Department, Sapienza University of Rome, for hospitality, and the Humboldt Foundation for financial support during part of this work.

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G.V., F.S., A.A., A.B., M.I., M.Z. and G.R. carried out the experimental work. A.R. and T.E. carried out the theoretical work. All authors contributed extensively to the discussion and interpretation of the data and results, and to the writing of the manuscript.

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Correspondence to M. Zaccanti.

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The authors declare no competing financial interests.

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Valtolina, G., Scazza, F., Amico, A. et al. Exploring the ferromagnetic behaviour of a repulsive Fermi gas through spin dynamics. Nature Phys 13, 704–709 (2017). https://doi.org/10.1038/nphys4108

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